DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 91: Hybrid Beta Limit at Low Rotation | ||
| Name: | C. Craig Petty ( |
Affiliation: | General Atomics |
| Research Area: | Core Integration (Advanced Inductive) | Presentation time: | Not requested | Co-Author(s): | -- |
| Description: | Determine the beta limit (most likely due to the onset of a 2/1 mode) for low rotation hybrid plasmas. Compare the beta limit to the ideal no-wall limit, and to the limit in rapidly rotating plasmas. First study q95=4.2, and if time permits study q95=3 and q95=5 as well. | ||
| Experimental Approach/Plan: | (1) Establish hybrid plasma with q95=4.2 using PCS feedback control of beta_N and rotation. (2) Use counter NBI to reduce rotation rate to minimal value. (3) Program a slow ramp up in beta_N to determine the stability limit (likely limit is onset of 2/1 mode). (4) Repeat beta_N ramp using only co-NBI. (5) If time permits, repeat at q95=3 and q95=5. | ||
| Background: | The bulk of hybrid study on DIII-D has been with co-NBI, producing rapid plasma rotation. For q95~4, the beta limit appears to coincide with the ideal no-wall stability limit. At q95~3, the beta limit is about 80% of the ideal no-wall limit. At q95~5, some hybrid plasmas have exceeded the ideal no-wall limit (probably owing to rotational stabilization). However, it is expect that in future larger devices like ITER the normalized rotation rates will be much smaller. Experiments in standard H-mode plasmas indicate that the beta limit decreases at lower rotation. Therefore, we need to measure the beta limits for low rotation hybrid plasmas at different q95 as part of our validation of this scenario for ITER. | ||
| Resource Requirements: | NBI: All 7 sources are required. | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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